And there were 3 million cancer survivors in 1971 and 9.8 million in 2001.

The study's authors note that the increase in number of cancer survivors is due to many factors, including a growing aging population, early detection, improved diagnostic methods, more effective treatment, and improved clinical follow-up after treatment.

“There is now a growing number of people who have faced a cancer diagnosis, which affects them and their loved ones – from the time of diagnosis through the rest of their lives," Julia Rowland, director of NCI's Office of Cancer Survivorship said in a statement.

“Unfortunately, for many cancer survivors and those around them, the effect of cancer does not end with the last treatment,” Rowland said. “Research has allowed us to scratch the surface of understanding the unique risks, issues, and concerns of this population. This report underscores the need for continued research.”